Among petroleum products, for example, lubricant oils, gas oils, jet fuels, and the like are products in which cold flow property is regarded as important. For this reason, it is desirable that base oils used for these products be such that waxy components such as normal paraffins or slightly branched isoparaffins, which are responsible for deteriorating the cold flow property, have been completely or partially removed, or converted to components other than waxy components.
An example of a known dewaxing technique for removing waxy components from hydrocarbon oils is a method wherein waxy components are extracted using a solvent such as liquefied propane or MEK. However, this method has problems in that the operating costs are high, and the product yield is reduced by the removal of waxy components.
A method for converting waxy components in a hydrocarbon oil to non-waxy components using a catalyst from the above solvent dewaxing process, a so-called isomerization dewaxing technique, is widely known as a method for improving the yield of a lubricant base oil.
On the other hand, an example of a known dewaxing technique for converting waxy components in a hydrocarbon oil to non-waxy components is isomerization dewaxing in which the hydrocarbon oil is contacted, in the presence of hydrogen, with a hydroisomerization catalysts having bifunction capable of hydrogenation-dehydrogenation and isomerization, thereby isomerizing normal paraffins in the hydrocarbon oil to isoparaffins (e.g., Patent Document 1).